1. Technical Field
The present invention relates to a method of manufacturing packages, a package, a piezoelectric vibrator, and an oscillator.
2. Description of the Related Art
In recent years, a piezoelectric vibrator (package) using crystal or the like as a time instance source, a timing source for control signals or the like, a reference signal source, and so on in mobile phone sets or portable digital assistant terminal devices is known. Various types of such piezoelectric vibrators are known, and a surface mount (SMD) type piezoelectric vibrator is known as one of these piezoelectric vibrators. The surface mount type piezoelectric vibrator includes a base substrate and a lid substrate formed of, for example, a glass material and joined to each other, and a cavity formed between these substrates, and a piezoelectric vibration reed (electronic component) stored in the cavity sealed in an air-tight manner.
In such a piezoelectric vibrator, a configuration in which through electrodes are formed in through holes formed in the base substrate, and the piezoelectric vibration reeds in the cavity and external electrodes out of the cavity are electrically connected via the through electrodes is known.
As a method of forming through electrodes, there is a method of filing the through holes formed on a base substrate with a conductive material such as silver paste or the like and baking the same.
However, with this method, since organic substance such as resin in the silver paste is removed by being baked and hence the volume is reduced, there is a case where depressed portions are formed on the surfaces of the through electrodes or the through electrodes are bored. The depressed portions or bores on the through electrodes may lead to lowering of hermeticity in the cavities or deterioration of conductivity between the piezoelectric vibration reeds and the external electrodes.
Accordingly, in recent years, a method of forming through electrodes by welding metallic pins in the through holes formed through the base substrate is developed (see JP-A-2003-209198). More specifically, through holes for allowing insertion of metallic pins are formed firstly heating the base substrate while pressing with a borer (primary forming). Subsequently, the base substrate is set in a forming die in a state in which the metallic pins are inserted into the through holes, and is heated in a state of being pressed (secondary forming). Accordingly, the melted base substrate (glass material) flows in the forming die and clogs up gaps between the metallic pins and the through holes, and the base substrate is welded to the metallic pins.
Incidentally, when manufacturing the piezoelectric vibrators, through electrodes are formed on a base substrate, then electrode films such as external electrodes which electrically connect the through electrodes and the outside and drawing electrodes which electrically connect the through electrodes and the piezoelectric vibration reeds are formed using Photolithography technique, Spattering method, or the like. Therefore, in order to ensure the continuity between the through electrodes and the electrode film, it is necessary to enhance the positional accuracy of the through electrodes (positional accuracy of the metallic pins) on the base substrate.
However, in the case of the method described above in the secondary forming, the metallic pins move in the forming die with the flow of the glass material (base substrate), so that the metallic pins may be welded in an inclined state or in a state of being displaced from desired positions. Therefore, there is a problem that the positional accuracy of the through electrodes is low.
In contrast, in JP-A-2003-209198, there is described a method in which metallic pins having a base portion and a core member extending from the surface of the base portion upright along the direction of a normal line are used and secondary forming is performed in a state of holding the base portions of the metallic pins in receiving portions formed in the forming die.
However, in order to store the base portions in the receiving portions smoothly at the time of clamping the forming die, it is necessary to set the diameter of the receiving portions to be sufficiently larger than the diameter of the base portions of the metallic pins. In this case, gaps are formed between inner peripheral surfaces of the receiving portions and side surfaces of the base portion. Therefore, in the secondary forming, the base portions move in the receiving portions, and hence significant improvement of the positional accuracy of the through electrodes (the positional accuracy of the metallic pins) cannot be expected.